Vehicle jacks are used in garages and body repair shops for examples, for lifting one or more wheels of a vehicle off the ground for carrying out repair or maintenance work on the vehicle. Vehicle jacks are sometime used by apprentices and inadvertent vehicle owners having more or less appreciation for the risks associated with the lifting of a vehicle and working under it. Conventional bumper jacks, axle jacks and scissors-type chassis jacks for examples are known to be unstable in certain circumstances and are generally not recommended for use without additional safety blocking. In that regard, clear written safety instructions are normally provided with the purchase of every vehicle jack. However, because of the inexperience of some users of vehicle jacks, and for other various reasons, proper vehicle lifting instructions are not always followed and users of vehicle jacks continue to be exposed to serious accidents.
In regard to improving the safety of vehicle jacks, a number of single-wheel jacks have been developed in the past. Some of these single-wheel jacks have a wheel tray for receiving a vehicle wheel and a broad base to prevent tilting of the jack when used on soft or uneven ground for example. Three models of single-wheel jacks of the prior art are described and illustrated in the following documents for reference purposes:
U.S. Pat. No. 3,292,902 issued on Dec. 20, 1966 to M. F. Lynch. The portable tire lift illustrated therein has a broad base, a lifting plate, a wheel tray mounted to the lifting plate and a scissors-type lifting mechanism connected to the broad base and to the lifting plate. A support post is mounted to the base and is engaged into a portion of the lifting plate. The post has vertically spaced-apart ridges for supporting the lifting plate and for preventing accidental collapsing of the lifting plate.
U.S. Pat. No. 3,784,161 issued on Jan. 8, 1974 to R. L. Frese. The wheel removal safety device illustrated therein is used for assisting in positioning a flat tire wheel at a certain height such that an axle jack or a bumper jack may be installed for removing and replacing the wheel. The device has a tilting plate forming an inclined surface on which the wheel is driven. The plate has a fulcrum at its centre point and is adapted to tilt and form an elevated horizontal surface when a wheel is driven thereon and moves pass the fulcrum. A conventional jack is then easily introduced under the elevated axle or bumper.
U.S. Pat. No. 5,503,368 issued on Apr. 2, 1996 to Manuel Torres. This patent describes a scissors-type wheel lift having broad base, a wheel tray and a scissors-type lifting mechanism connected to the wheel tray and to the broad base, for lifting the wheel tray. The wheel lift is used in combination with a ramp having a height corresponding to the height of the wheel tray when the wheel tray is in a collapsed mode. In use, a wheel is driven over the ramp and into a wheel tray. A hand crank and a screw are used to operate the scissors-type lifting mechanism.
It has been found that a common problem with the lifting of a vehicle with a jack is that a partial raising of a vehicle, on one corner or on one end of the vehicle, causes the whole vehicle to be pulled toward the jack. Therefore, when the wheel being lifted is not properly retained inside the wheel tray of a jack, or when one of the supporting wheels is chocked against the jack, the wheel being lifted tends to roll out of the wheel tray, thereby causing a hazardous condition.
Another problem with scissors-type lifting mechanisms of single-wheel jacks of the prior art is that the mechanism has a substantial vertical thickness. Modern compact vehicle have relatively small diameter wheels, of 14 and 15 inches for examples. These wheels are often too small to afford a smooth rolling over the scissors-type lifting mechanism and into the wheel tray of these vehicle jacks.
It is believed that these problems basically, have contributed to cause significant obstacles to the commercial success of the wheel-tray-type jacks of the prior art. It is further believed that there continues to be a need for a better single-wheel jack capable of being used easily and safely by the experienced tradesmen as well as by the hobby-time auto-mechanics.